1. Institute for Fusion Studies and Department of Physics, The University of Texas, 1 University Station C1500, Austin, Texas 78712, USA
2. P.N. Lebedev Physics Institute, Moscow, Russia
3. Center for Fundamental and Applied Research, Dukhov Research Institute of Automatics (VNIIA) ROSATOM, Moscow, Russia
4. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14850, USA